SQL，CROSS JOIN速度优化

问题其实在于下面SQL的string1_emb和string2_emb的数据传输是速度瓶颈

            SELECT  /*+ MAPJOIN(a2) */
                    a1.string1
                    ,a2.string2
                    ,a1.string1_emb
                    ,a2.string2_emb
            FROM    (
                        SELECT  string1
                                ,string1_emb
                        FROM    table1
                    ) a1
            CROSS JOIN  (
                            SELECT  string2
                                    ,string2_emb
                            FROM    table2
                        ) a2    

改成先cross join的时候只string1和string2，再on string1/string2 inner join上embedding

            SELECT  /*+ MAPJOIN(a2) */
                    a1.string1
                    ,a2.string2
            FROM    (
                        SELECT  string1
                        FROM    table1
                    ) a1
            CROSS JOIN  (
                            SELECT  string2
                            FROM    table2
                        ) a2